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High Angular Resolution Study of the Earliest Stages of Star Formation [ Phd THESIS ]

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High Angular Resolution Study of the Earliest Stages of Star Formation [ Phd THESIS ] UNIVERSIDAD DE GRANADA Tesis doctoral Julio 2010 High angular resolution study of the earliest stages of star formation [ PhD THESIS ] Carlos Carrasco Gonz´alez Instituto de Astrof´ısica de Andaluc´ıa (CSIC) Memoria de Tesis presentada en la Universidad de Granada para optar al grado de Doctor en F´ısica Director de tesis: Guillem Anglada Pons Editor: Editorial de la Universidad de Granada Autor: Carlos Carrasco González D.L.: GR 3519-2010 ISBN: 978-84-693-5350-9 . A mis padres. Agradecimientos El trabajo de Tesis que aqu´ıse presenta es el resultado de 4 a˜nos de trabajo. Afortunada- mente, durante todo este tiempo nunca he estado solo. Muchas personas han participado de este trabajo. Algunas las he ido encontrando en el camino, otras siempre han estado ah´ı. A todas estas personas les agradezco sinceramente todo el apoyo que me han brindado. A mi director de Tesis, Guillem Anglada, por haberme introducido en el mundo de la radioastronom´ıa, por todos los conocimientos que me ha transmitido, y por la inmensa ayuda que me ha prestado en todo momento durante la realizaci´on de este trabajo, que es tan suyo como m´ıo. A Luis Felipe Rodr´ıguez, con quien he tenido la gran suerte de trabajar estrechamente, por hacer tan f´aciles, cosas que parec´ıan tan complicadas. A todas las personas que, con su colaboraci´on, han hecho posible la escritura de muchas de las p´aginas de esta Tesis: Antxon Alberdi, Jos´eFco. G´omez, Rosario L´opez, Josep Mart´ı, Mayra Osorio, Jos´eMar´ıa Torrelles. A mis compa˜neros del IAA; A los miembros del Triunvirato: Dar´ıo, Dani y Miguel Angel,´ por todas las discusiones “cient´ıficas” que hemos tenido, siempre, en la barra de un bar, siempre, sobre “la vida”; A Omaira, por seguir estando ah´ı; A las ni˜nas del 547: Yoli y Tere (Amparito!!), por cuidarme a Gaby; A la (ahora) ni˜na del 598: Marti˜na, por ser ´unica. A Juanma, por compartir conmigo sus reflexiones sobre... sobre todo. A toda las personas del CRyA, que me hicieron tan f´acil el estar tan lejos de casa: Karla Alamo,´ Roberto Galv´an, Yolanda G´omez, Vicente Hern´andez, Jes´us Toal´a, Rosy Torres. A mis padres, quienes, con su apoyo incondicional, son los verdaderos responsables de que yo est´eescribiendo esto hoy. Y a mi hermanita!!, que creo que es la persona que m´as ha creido en m´ı. Y por ´ultimo, gracias a t´ı, Gabriela, por haberte cruzado en mi camino, por haber decidido recorrerlo conmigo haci´endolo infinitamente m´as f´acil, por hacerme re´ır cuando lo necesito, y en definitiva, por hacerme tan feliz compartiendo tu vida conmigo. Carlos Carrasco Gonz´alez, 9 Julio de 2010 . Resumen En esta Tesis se presenta un estudio observacional con alta resoluci´on angular de las primeras etapas de la formaci´on estelar, con especial ´enfasis en el fen´omeno de los jets y de los discos protoplanetarios. El estudio se ha realizado mediante observaciones obtenidas con los radiointer- fer´ometros Very Large Array (VLA), Combined Array for Research in Millimeter-wave Astron- omy (CARMA), y Sub-Millimeter Array (SMA). Se han estudiado cinco regiones de formaci´on estelar: dos regiones de formaci´on estelar de baja masa (L723 y HL/XZ Tau), una regi´on de formaci´on estelar de masa intermedia (NGC 2071) y dos regiones de formaci´on de alta masa (W 75 N y HH 80-81). Hemos llevado a cabo observaciones de alta resoluci´on angular con el VLA a 3.6 cm y 7 mm hacia la regi´on del flujo molecular multipolar en L723, donde hemos encontrado un sistema m´ultiple de objetos estelares j´ovenes en una regi´on con una extensi´on de s´olo 1200 UA. Dos de estos objetos (VLA 2A y VLA 2B) forman un sistema binario con una separaci´on de 90 UA. Hemos propuesto que el flujo molecular multipolar de CO observado en L723 podr´ıa ser el resultado de la superposici´on de, al menos, tres flujos bipolares independientes, impulsados por tres objetos j´ovenes distintos. Nuestras observaciones sugieren que VLA 2A est´aasociada con un radiojet y que es la fuente que impulsa el sistema de objetos Herbig-Haro (HH) previamente detectado en la regi´on, as´ıcomo uno de los flujos moleculares de CO. Proponemos que VLA 2B es la fuente que impulsa el segundo flujo de CO. Finalmente, un tercer flujo de CO parece ser un flujo “fosil” cuya fuente de energ´ıa no ha estado muy activa en el pasado reciente. Observamos la emisi´on de polvo a 7 mm asociada con la estrella joven HL Tau. Esta emisi´on parece provenir de un disco con un radio de ∼25 UA. En este disco, hemos detectado un hueco a un radio de ∼10-15 UA (similar al radio de la ´orbita de Saturno) que podr´ıa ser un signo de la formaci´on de un protoplaneta. Estas observaciones tambi´en han puesto de manifiesto que la estrella joven XZ Tau, que hab´ıa sido previamente identificada como un sistema binario con una separaci´on de 42 UA, es realmente un sistema triple, ya que nuestras observaciones han resuelto una de las dos componentes en un sistema binario de 13 UA. Hemos propuesto que la eyecci´on de gas observada con el HST en esta estrella puede estar relacionada con el paso por el periastro de las componentes del nuevo sistema binario. Estudiamos la emisi´on en el rango centim´etrico (libre-libre) y milim´etrico (polvo) de las fuentes infrarrojas en el centro de la regi´on de formaci´on estelar NGC 2071. La emisi´on de la fuente IRS 1 presenta una morfolog´ıa alargada con protuberancias en ambos extremos. Hemos interpretado esta fuente como un radiojet que interacciona fuertemente con el medio o, alter- nativamente, como dos radiojets impulsados por un sistema binario. Nuestras observaciones de mayor resoluci´on angular del centro de la emisi´on muestran un indicio de una fuente doble, lo que sugiere la posible presencia de un sistema binario. La emisi´on en el centim´etrico de la fuente IRS 3 en NGC 2071, traza un radiojet ionizado, mientras que la emisi´on en el milim´etrico traza un disco circunestelar orientado perpendicularmente al jet. Esta orientaci´on de la emisi´on milim´etrica coincide con la orientaci´on de los m´aseres previamente observados por Torrelles et al., y que fueron interpretados como un disco de acreci´on circunestelar. Hemos modelado la viii emisi´on del polvo del disco de acreci´on, lo que nos ha permitido restringir el radio y la tasa de acreci´on del disco, as´ıcomo la masa de la estrella central. Hemos estudiado la naturaleza y el entorno de las fuentes de radio en la regi´on W 75N. Nuestros resultados apoyan fuertemente que la fuente VLA 3 es un radiojet asociado con un objeto estelar joven. Hemos detectado importantes variaciones en la densidad de flujo, mor- folog´ıa y posici´on de la fuente Bc, lo que sugiere que esta radiofuente no est´atrazando una estrella independiente, sino que es realmente un objeto HH impulsado por VLA 3. Si nuestra interpretaci´on es correcta, ´este es uno de los objetos HH radio m´as intensos conocidos hasta ahora. Nuestras observaciones de la emisi´on molecular de amon´ıaco a gran escala muestran que la formaci´on estelar en W 75 N podr´ıa estar desencadenada por la colisi´on de dos nubes moleculares filamentarias. Hemos observado la fuente que impulsa el jet HH 80-81 con el VLA y el SMA. Hemos detectado emisi´on de la mol´ecula de SO que sugiere la presencia de gas molecular orbitando en torno a ella. A partir de estas observaciones, estimamos un l´ımite inferior de 17 M⊙ para la masa central. La densidad de flujo y morfolog´ıa cuadrupolar de la emisi´on a 7 mm asociada con la fuente de energ´ıa del jet, sugiere que es una combinaci´on de emisi´on libre-libre del radiojet y emisi´on de polvo de un disco circunestelar perpendicular al jet. Hemos modelado con ´exito la emisi´on a 7 mm como un disco de acreci´on con un radio de 420 UA, una tasa de acreci´on de −6 −1 7×10 M⊙ yr y una masa de 14 M⊙ orbitando alrededor de una estrella de 10 M⊙. Hemos realizado observaciones de muy alta sensibilidad a 6 cm del jet de HH 80-81 que revelan que la emisi´on en los l´obulos del jet situados a ∼0.5 pc de la fuente central, est´a linealmente polarizada, confirmando su naturaleza como radiaci´on sincrotr´on, lo que implica la presencia de electrones relativistas y un campo magn´etico asociado con el jet. A partir de nuestras observaciones hemos podido inferir la estructura del campo magn´etico en el jet de HH 80-81, de modo an´alogo a como se hace en los jets extragal´acticos, que se caracterizan por su intensa emisi´on sincrotr´on. Nuestro descubrimiento de radiaci´on sincrotr´on en un jet asociado a una estrella joven representa un paso importante en la unificaci´on del fen´omeno de los flujos colimados observado que se observa en muchos contextos astrof´ısicos. Summary In this thesis, we present an observational, high angular resolution study of the earliest stages of the star formation process, with a special emphasis in the phenomena of jets and protoplanetary disks.
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